1. Field of the Invention
The present invention relates to an observation apparatus, and in particular to an observation apparatus for observing patterns such as circuits and characters formed in the surface or near the surface of semiconductor wafers and insulation substrates such as glass, ceramic and the like.
2. Description of the Prior Art
Up to now, during the manufacturing process of semiconductor integrated circuits, observation of patterns such as numbers, characters and circuits provided on the surface of semiconductor wafers (hereinafter referred to simply as xe2x80x9cwaferxe2x80x9d), liquid crystal substrates, glass, ceramic or resin have been carried out by direct visual inspection or by the use of a camera or microscope. For example, during the manufacturing process, the identification code provided on a wafer are read, and then a predetermined process is carried out in accordance with such identification code.
In observation devices known in the prior art, light source of a fluorescent lamp, fiber optics illumination or a parallel light source through a lens is used to illuminate an observation object in order to perform observation.
In this connection, the present inventor previously proposed (in Japanese Laid-Open Patent Application No. HEI-8-327554) an illumination device for obtaining a high-contrast image, in which light from a light emitting portion is shone by means of an optical element onto an observation object, with the light emitting portion being movable with respect to the optical element in order to make it possible to adjust the illumination angle of the light shining onto the observation object.
With the invention described above, remarkable results were obtained when the light emission portion was moved to obtain optimum illumination, but it isn""t always clear which way the light emission portion should be moved to obtain optimum illumination. Thus, it is an object of the present invention to provide a light source arrangement which makes it easy to obtain an optimum illumination.
In this connection, FIG. 1 shows the principle of the observation apparatus according to the present invention for overcoming the problems described above. As shown in this drawing, the observation apparatus shines light from a light source through an optical element (converging lens 11) and onto an observation object 3a, and a light source portion 13 is equipped with a first light-emitting body 13a, second light-emitting bodies 13b, third light-emitting bodies 13c and 13d and fourth light-emitting bodies 13e, and all these light-emitting bodies are arranged at or near the optical axis 11b of the converging lens 11 within a light source plane 110a arranged at or near the front focal position of the converging lens 11. Further, the light-emitting bodies 13axcx9c13e are selectively activated to illuminate the observation object 3a, and the light reflected from or passing through the observation object is received by a light-receiving portion 7a to be used in observing the observation object 3a. 
If the light emitted from any one of the light-emitting bodies strikes the observation object 3a at an incidence angle xcfx86 with respect to the optical axis 11b, then the incidence angle xcfx86 will become larger as the distance between the light-emitting body and the optical axis 11b increases. In this regard, the incidence angle xcfx86 is easily measured based on the focal point distance of the converging lens 11 and the position of the light-emitting body.
The first light-emitting body 13a is arranged on the optical axis 11b, and the second, third and fourth light-emitting bodies are arranged at increasing distances away from the optical axis 11b in that respective order. In this connection, FIG. 2 is a series of drawings showing the relationship between light source images 14axcx9c14e of each of the light-emitting bodies and the light-receiver portion 7a and the image of the observation object 3a formed on the light-receiver portion 7a. Namely, the light source images 14a, 14b, 14c, 14d and 14e correspond respectively to the light source images of the light-emitting bodies 13a, 13b, 13c, 13d and 13e. In this regard, each of the light-emitting bodies carries out the following illumination.
(1) In general, in bright field illumination, if the observation object 3a and the observation plane were a plane mirror, the light from the light-emitting body arranged on the optical axis of the converging lens would reflect off such plane mirror and pass through an image-forming lens 17 at the light-receiving side along a direction aligned with the optical axis of the image-forming lens 17, whereby the light source image will illuminate the entire surface of the light-receiving portion. In the present invention, the first light-emitting body 13a carries out this type of illumination, and the light source image at such time is like that shown in FIG. 2A. Now, in the case where this type of illumination is to be used for characters formed in a wafer by laser etching or the like, if there is no image noise, such characters will generally be observed as dark forms in the shining light source image. However, if there are slight irregularities on the wafer or resist, it is possible for such irregularities to be observed as dark lines (image noise).
(2) By moving the light source to a position slightly away from the optical axis without changing the state in which the light source image covers the entire surface of the light-receiving portion, the present inventor discovered that it is possible to eliminate the dark lines (image noise) due to the above-mentioned irregularities. In the present invention, the second light-emitting bodies 13b carry out this type of illumination, with a light source image being formed as shown in FIG. 2B. In this way, there is also a bright field illumination state in which the light source is positioned slightly away from the optical axis, and it was confirmed that this type of illumination makes it possible to eliminate image noise. The incidence angle xcfx86 of this illumination depends on many conditions of the optical system, but a value around xcfx86=20xc2x0 serves as a good example.
(3) The third light-emitting bodies 13c and 13d are positioned farther away from the optical axis than the light-emitting bodies 13b, with the light-emitting bodies 13d being positioned farther away from the optical axis than the light-emitting bodies 13c, and the incidence angles of the light emitted from the light-emitting bodies 13c and 13d cause their respective light source images 14c and 14d to cover only a partial portion of the light-receiving portion 7a, as shown in FIGS. 2C and 2D. As for the difference between the illumination of the light-emitting bodies 13c and the light-emitting bodies 13d, it should be noted that illumination by the light-emitting bodies 13c involves light from the light source striking the observation object 3a (hereinafter referred to as xe2x80x9cincomplete bright field illuminationxe2x80x9d; see FIG. 2C), and illumination by the light-emitting bodies 13d involves light from the light source not striking the observation object 3a (hereinafter referred to as xe2x80x9cincomplete dark field illuminationxe2x80x9d; see FIG. 2D). In this connection, either of these types of illumination were not used in the prior art because they were considered as incomplete illumination. However, the present inventor confirmed that even with these types of incomplete illumination, it is possible to obtain optimum contrast depending on the properties of the observation object and the incidence angle from the light source. The incidence angle xcfx86 of these types of illumination depend on many conditions of the optical system, but a value around xcfx86=5xc2x0 serves as a good example for the case of incomplete bright field illumination (light-emitting bodies 13c), and a value around xcfx86=7xc2x0 serves as a good example for the case of incomplete dark field illumination (light-emitting bodies 13d).
(4) The fourth light-emitting bodies 13e are positioned farther away from the optical axis than the light-emitting bodies 13d, and because the light source image 14e doesn""t cover any of the light-receiving portion 7a (see FIG. 2E), the fourth light-emitting bodies 13e carry out a dark field illumination. With this type of illumination, the background is dark and the character or pattern portion appears bright. The incidence angle xcfx86 of this type of illumination also depends on many conditions of the optical system, but a value around xcfx86=10xc2x0 serves as a good example.
Further, by selectively activating specific light-emitting bodies among the plurality of light-emitting bodies described above, it is possible to obtain an excellent high-contrast image.
In the present invention, all the light-emitting bodies from the plurality of light-emitting bodies may be used, or only the first, second and fourth arrangement of light-emitting bodies may be used. Furthermore, it is possible to use only the first, third and fourth light-emitting bodies or only the third light-emitting bodies. Further, even thought the third arrangement of at least one light-emitting body is described as having the two sets of light-emitting bodies 13c and 13d, it is possible to provide the third arrangement with only a single set of light-emitting bodies.
As described above, by specifying the light source arrangement, it becomes possible to reliably determine the optimum light source position, and this makes it possible to easily obtain an excellent high-contrast image.